Take off the foliage with the botrytis on carefully so you don't spread the spore, then give a few puffs of yellow sulphur ( you can find this at most garden centres ) go really easy with any watering as botrytis loves damp conditions then hopefully you should be ok.If its not logical to take the foliage off just use the sulphur and hopefully this will still work.

if I'm storing any barefoot plants over winter, before I put them to store I always use sulphur.